This invention relates generally to a corona generating device, and more particularly concerns a method and apparatus for determining altitude with a corona generating device, in order to adjust xerographic settings.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith.
Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are extracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet. In printing machines such as those described above, corona devices perform a variety of other functions in the printing process.
For example, corona devices aid the transfer of the developed toner image from a photoconductive member to a transfer member. Likewise, corona devices aid the conditioning of the photoconductive member prior to, during, and after deposition of developer material thereon to improve the quality of the electrophotographic copy produced thereby. Both direct current (DC) and alternating current (AC) type corona devices are used to perform these functions. One form of a corona charging device comprises a corona electrode in the form of an elongated wire connected by way of an insulated cable to a high voltage AC/DC power supply.
The scorotron is similar to the pin corotron, but is additionally provided with a screen or control grid disposed between the coronode and the photoconductive member. The screen is held at a lower potential approximating the charge level to be placed on the photoconductive member. The scorotron provides for more uniform charging and prevents over charging.
A problem with xerographic printing systems is that these systems are affected by the environment in which these system are placed. For example, detack corotron AC voltages are required for different altitude conditions to obtain optimal performance of the xerographic printing systems. In U.S. Pat. No. 6,266,494 teaches that in any xerographic development system in which there is a substantial potential relative to the photoconductive, but particularly when there exists an alternating current field across a development gap, there is a practical risk of arcing across the gap. Such arcing will of course have a deleterious effect on the operation of the printing apparatus, causing at the very least a print defect and at worst damage to the apparatus. The various control systems for maintaining print quality in any xerographic printing apparatus are liable to cause the various potentials associated with the xerographic process to reach such levels that arcing is possible. The risk of arcing is particularly increased in situations where the printing apparatus is installed at high altitudes, such as in mountainous regions. The relatively low air pressure at higher altitudes can lead to Paschen breakdown, that is, the ionization of air molecules which leads to arcing, at much lower potentials than would occur at lower altitudes.
Hereinbefore, xerographic printing systems capable of being adjusted for different altitudes require the service operator to look up the altitude and input the value for setting machine parameters. Therefore, it is desirable to be able to easily determine and input the altitude of the xerographic printing systems without operator intervention.
There is provided a method for determining an altitude with a corona generating device having a grid and a coronode and a power supply for supply power to said grid and coronode, comprising: setting the grid at a predefined voltage with the power supply; applying a charge output voltage and a charge output current to the coronode with the power supply; monitoring the charge output voltage and the charge output current to the coronode from the power supply until a predefined charge output voltage is reached; correlating charge output current to an altitude when said predefined charge output voltage is reached.
There is also provided an electrostatic printing machine having a method for determining an altitude with a corona generating device having a grid and a coronode and a power supply for supply power to said grid and coronode, comprising: setting the grid at a predefined voltage with the power supply; applying a charge output voltage and a charge output current to the coronode with the power supply; monitoring the charge output voltage and the charge output current to the coronode from the power supply until a predefined charge output voltage is reached; correlating charge output current to an altitude when said predefined charge output voltage is reached.